Year	Years
1970	0.37
1971	0.38
1972	0.39
1973	0.41
1974	0.42
1975	0.44
1976	0.45
1977	0.47
1978	0.48
1979	0.5
1980	0.51
1981	0.53
1982	0.55
1983	0.57
1984	0.59
1985	0.61
1986	0.63
1987	0.65
1988	0.67
1989	0.69
1990	0.72
1991	0.74
1992	0.77
1993	0.79
1994	0.82
1995	0.85
1996	0.88
1997	0.91
1998	0.94
1999	0.97
2000	1
2001	1.04
2002	1.07
2003	1.11
2004	1.15
2005	1.18
2006	1.22
2007	1.26
2008	1.3
2009	1.35
2010	1.39
2011	1.44
2012	1.48
2013	1.53
2014	1.58
2015	1.63